1. Field of the Invention
This invention relates to so-called jacks and lifting devices by which heavy or awkward objects may be raised from a primary supporting surface during repair or construction. More particularly, the invention relates to an effective jack or lifting device for lifting doors into position during so-called "hanging" of such doors, particularly in new construction, but also in existing construction.
2. Prior Art
When mounting swing-type doors in a building, the door must not only be very accurately made to fit the door frame, but also must be accurately held in place in the door frame both while the hinges and sometimes locks are being affixed to the door and the frame, but also in most cases, while the hinge and lock position is being measured or laid out prior to actual affixation of the hinges and lock on the door. Customarily, the door is first carried to the door opening into which it is to be inserted and is manually raised into position and held temporarily in place by means of shims or small wedges of wood or the like while being measured or while being mounted or attached to the door frame. Sometimes nails have been driven into the floor under where the door is to be mounted at both sides of a door frame with their heads at the calculated height of the bottom of the door to support such door while being mounted in place. Both shims and nails in the floor tend to damage the floor, however, particularly in the case of supporting nails. The hanging operation has traditionally been a two-man operation in which a carpenter or other skilled workman marks the door and shims it into exact position while a carpenter's helper holds the door in place or actually shims it into place by forcing slanted shims under it until the carpenter indicates such door is in exact position. Accurate fitting and hanging of a door is skilled labor, the successful completion of which has a large effect upon the quality of a building as well as the perception of the quality of a building.
While the trend has been to the use of lighter doors and particularly hollow or foam plastic insulated metal doors and the like for residential construction, at the same time in industrial and commercial establishments there has been a noticeable trend to heavier doors, some of which may weigh hundreds of pounds or even more. In such installations the difficulty in hanging the door is often multiplied by a factor of two or more up to as much as ten or more. Even very light doors, however, present a serious problem with respect to holding in place during installation, because a single workman has at most only two arms and hands to both hold a door in place and work on it at the same time during installation.
So-called door jacks for lifting into position a door during hanging of such door have been invented or developed before, but none, so far as the present inventor is aware, have come into widespread use. Some of such jacks have been provided with wheels or other sliding arrangements so that a door may not only be raised into proper position in the door frame, but also may be basically rolled or slid horizontally into position by a single worker. Typical of some of the prior art devices are those shown and described in the following patent documents.
U.S. Pat. No. 604,833 issued May 31, 1898 to R. Muller discloses a lever-type lifting device mounted upon a roller-like bottom block and having a downwardly curved door support on one end for slipping under a door. The lever may also be mounted upon a separate lower mounting or shore piece to apparently provide stability of the lever during use. The device is designed for partial unhinging of a door to more effectively oil or lubricate the hinges of such door.
U.S. Pat. No. 671,554 issued Apr. 9, 1901 discloses a door or window lifter comprising a base having a curvilinear lever pivoted between two pivot arms extending upwardly from the base. A lever catch arrangement is provided at the rear of the device to fix the lever in an upwardly biased position to hold a door or window in a single elevated position.
U.S. Pat. No. 1,681,834 issued Aug. 21, 1928 to A. A. Arends discloses a door-holding or lifting tool comprised of a sort of sliding crowbar arrangement with preferably a tooth end and a fulcrum block, preferably having a rubber fulcrum on the bottom and two pivoted brace bars on the top which aid in holding the door in place while supported on the upturned end of the lowered crowbar section.
U.S. Pat. No. 1,833,005 issued Nov. 24, 1931 to W. F. Staggers discloses a door-holding device comprised essentially of a flat holding or supporting bar having upstanding teeth on the top surface for engaging a door, plus a set of wheels at one end pivoted upon a base with a handle which may be pivoted to a position in which the tooth carrier bar lies flat upon the floor and a series of positions in which it is pivoted upwardly at one end to raise the door into various vertical positions or elevations from the floor. The door is supported crosswise to the longitudinal length of the supporting bar upon which it rests.
U.S. Pat. No. 2,682,076 issued Jun. 29, 1954 to S. O. Christensen discloses a mechanical apparatus for both elevating and shifting a boxcar door laterally or horizontally by means of a device including a roller and a pivotable handle that exerts leverage to raise the door so it can then be slid sidewise on its normal track. The device is not constructed for temporary support of a door while working on it, but for use in first raising a boxcar door from its closed and locked position into the raised position in which it may move along the door track supplied for opening of such door.
U.S. Pat. No. 3,871,054 issued Mar. 18, 1975 to T. S. Schaefer discloses a U-shaped, two-wheel, door-transporting dolly which can be used to lift the door into place by canting the frame of the dolly with the foot.
U.S. Pat. No. 3,642,251 issued Feb. 15, 1972 to F. J. G. Niederholtmeyer discloses a crowbar-type door lifter or adjuster having a side rest bar at the top of the crowbar section to stabilize the upright position of the door while canting the crowbar to lift the door.
U.S. Pat. No. 4,043,536 issued Aug. 23, 1977 to L. T. Almond discloses a wheeled dolly for transporting doors having a handle for wheeling the door into place and a foot incline or lanyard for depressing the handle to lift a carrying ledge on the dolly to lift, or elevate, and support the door in place.
U.S. Pat. No. 4,712,771 issued Dec. 15, 1987 to K. S. Donnelly discloses a rectangular pivoted-type wallboard jack in which the wallboard rests on a thin lip at the edge of the pivoted section of the jack and is lifted by depressing the opposite end of the jack.
British Specification 999,839 dated Jul. 8, 1964 to Scaffolding Limited discloses a lifting and transporting jack comprising a wheeled dolly with a handle between the wheels and having a lifting lip in the front.
British Specification 2,225,679 dated Jun. 13, 1990 to W. R. Kashey discloses a flat base with a pivoted lever arm pivotally supported on top having said lever arm having a forward ledge for support and adjustment of a door or window. The height of such door or window in the frame is controlled by an inclinable screw-threaded biasing member having a handle on top. The threaded adjustment includes a threaded female fitting that threads onto an inclinable male threaded member and exerts downward force upon one end of the pivotable member.
While the available prior art devices, as summarized by the above-described patent documents, have been effective to a point, they have not been as efficient as could be hoped. There is a clear need, therefore, for an improved practical apparatus for accurately supporting doors, including relatively massive doors and the like, while hanging such doors, which device can be easily and effectively used by a single workman, eliminating the usual necessity to have at least two and possibly more workmen hanging such doors.